Solutions

Negative emissions technologies are the solution set we must build to achieve deep and lasting removal of carbon dioxide already in the atmosphere.

The term ‘NETs’ is used to describe a diverse range of technical solutions that remove and store atmospheric carbon. Some involve physical plant and equipment, others involve innovative practices or enhanced natural processes.

Afforestation / reforestation and land regeneration

Implementation options:

  • Agro-forestry
  • Boreal
  • Temperate
  • Tropical

Earth system:

  • Land

Storage medium:

  • Above-ground biomass

Replanting and regeneration of cleared and/or degraded lands. Includes agroforestry integration of complementary tree species in other land uses.

CO2 is captured through photosynthesis and plant respiration and stored in above ground biomass and soil for as long as forests are stable.

Biochar

Implementation options:

  • Crop residues
  • Dedicated crops
  • Dedicated crops (marginal)

Earth system:

  • Land

Storage medium:

  • Soil

CO2 is captured through photosynthesis of purposefully grown biomass which is harvested and converted into biochar through pyrolysis and stored as soil carbon through mineralisation and as woody biomass. Biochar can be integrated with other land remediation removal activities to improve water retention and microbial activity.

Bioenergy with carbon capture & storage (BECCS)

Implementation options:

  • Crop residues
  • Dedicated crops
  • Dedicated crops (marginal)

Earth system:

  • Land

Storage medium:

  • Geological resivours

Combination of bioenergy for electricity/industrial heat generation, with point source carbon capture and storage (CCS). Atmospheric CO2 is captured through photosynthesis of purposefully grown biomass, which is then combusted for heat/power, and CO2 is re-captured through and geologically stored through CCS.

Direct air capture with carbon capture and storage (DAC+CCS)

Implementation options:

  • Suspended amines
  • Wet calcination

Earth system:

  • Land

Storage medium:

  • Geological resivours

DAC units mechanically pass air over reactive compounds to chemically trap and extraction CO2 for separate storage. CO2 is captured through reaction with wet lime solvents/dry amine sorbents, which are then heated to extract the CO2 for geological storage in CCS wells. Next generation DAC research is focused on passive DAC units and molecular filters using membranes or metal organic frameworks.

Accelerated weathering – Land remediation

Implementation options:

  • Silicate rocks

Earth system:

  • Land

Storage medium:

  • Minerals

Accelerated weathering through the application of mafic rock dust (e.g., basalt) to croplands and degraded soils. Magnesium and calcium silicates react with CO2 in moisture to form stable mineral carbonates in the soil and/or support ocean alkalisation through run off.

Accelerated weathering - Ocean alkalinity enhancement

Implementation options:

  • Carbonate rocks
  • Silicate rocks

Earth system:

  • Ocean

Storage medium:

  • Minerals

Accelerated weathering through the addition of crushed mafic (e.g., basalt) or ultramafic (e.g. olivine) minerals to seas and oceans. Magnesium and calcium silicates produce bicarbonate ions in a buffering reaction. This reduces ocean acidity caused by dissolved CO2. Oceans then remove and store further CO2 from the atmosphere.

Ocean alkalinity enhancement with ultra-green (carbon negative) hydrogen

Implementation options:

  • Carbonate rocks
  • Silicate rocks

Earth system:

  • Ocean

Storage medium:

  • Minerals

Augmentation of green hydrogen electrolysis processes to produce alkaline wastewater to be used for ocean alkalinity enhancement, in addition to production of hydrogen. The process reacts silicate (e.g., olivine) or carbonate (e.g., limestone) minerals with acidic water from the electrolysis process, to produce alkaline hydroxide ions. Like accelerated weathering, this alkalinity can then be used to reduce ocean acidification and store more CO2 from the atmosphere.

Iron ocean fertilisation

Implementation options:

  • Iron fertilisation

Earth system:

  • Ocean

Storage medium:

  • Marine sediment and calcifers

Adding iron to trace-element depleted oceans (e.g., the Southern Ocean) to boost natural carbon removal from surface waters by photosynthesising plankton populations. Storage occurs if additional carbon fixed by phytoplankton can be made to sink into the deep ocean.

Mine site carbon mineralisation

Implementation options:

  • Mine sites

Earth system:

  • Land

Storage medium:

  • Minerals

Accelerated reaction of CO2 with ultramafic mine tailings (e.g., serpentinite, dunnite). Combinations of water, temperature and biotic and abiotic catalysts are used to react magnesium and calcium silicates with dissolved atmospheric CO2 to form stable mineral carbonates that are stored in remediated mine sites.

Carbon negative cropping & grazing

Implementation options:

  • Agricultural practices

Earth system:

  • Land

Storage medium:

  • Soil

Includes land recontouring for precipitation retention, improved perennial crops and grasses, cropping, high carbon input crop phenotypes, improved tillage, improved grazing land management.

CO2 is captured through photosynthesis and plant respiration and stored in above ground biomass and soil, while plant systems are stable.

Macro algae cultivation

Implementation options:

  • Aquaculture practices

Earth system:

  • Ocean

Storage medium:

  • Under-ocean biomass

Managed cultivation of large scale macroalgae (e.g., kelp) plantations in coastal sediments or on offshore engineered structures.

CO2 is captured through photosynthesis and converted into biomass. It is either stored in algae ecosystems as living biomass, or deliberately sunk in the deep ocean where it is isolated from the atmosphere for centuries or longer.

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